Can EX relay/forward email if the mailbox was not found?

Hi,
Can I set the following in EX2013: If email arrives-in for an authoritative domain but the specific mailbox doesn't exist, then forward or relay to another custom server/smart host (the custom server is not EX server)?

For example, our domain is: something.com, I want that if email arrives to: nonexisting+mailbox@something.com it will be forwarded to custom, not Exchange, server we have in our network.

Is this possible?

Thanks,
Yonatan

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